The following application is related to the present application: U.S. Patent Application entitled xe2x80x9cMETHOD AND APPARATUS FOR RAPID, SYNCHRONIZED, AND ISOLATED TRANSISTOR SWITCHING,xe2x80x9d attorney docket number 10990467-1, naming Daniel F. Mulhauser as the inventor, assigned to the assignee of the present invention, and filed concurrently herewith.
The present invention relates generally to methods for operating transformer circuits and, more particularly, to methods and circuits for providing control signals to primary windings of transformers.
Methods have been designed for applications in which switching devices must stand off and supply high voltages, and in which rapid switching (e.g. in the range of microseconds or faster) is required. One of these applications, connecting a traveling wave tube to its high voltage cathode supply, is described in U.S. Pat. No. 4,754,176 to Jones, et al. As noted in Jones, switching transistors are preferred in these applications, as compared, for example, to mechanical relays, due to the requirements for rapid switching. In addition, it may be desirable to employ a number of switching transistors in series in order to overcome limitations on the amount of voltage that a single device can handle. Connecting the switching transistors in series typically imposes the additional requirements that the driving circuits of the transistors be electrically isolated from each other, and that the switching be synchronous. Jones accomplishes the isolation and synchronous switching of series-connected transistors by employing one transformer for turning the switches on (labeled 200 in FIG. 2, driven by transistor Q1), and another transformer for turning the switches off (unlabeled, driven by transistor Q2).
Another application in which high voltages must be rapidly switched is in the use of external heart defibrillators. These devices supply controlled electrical pulses that are applied to the chests of patients in cardiac arrest. Defibrillators may also be implanted, in which case the electrical pulses are applied directly to the heart and the voltages to be switched naturally are much smaller. Older external defibrillators typically used mechanical relays as the switching devices. Defibrillators that are more modern typically use solid state methods having power transistors to switch the high voltages. These power transistors may be metaloxide semiconducting, field-effect transistors (MOSFET""s), insulated gate bipolar transistors (IGBT""s), or similar known devices.
In one aspect of the present invention, a method is disclosed for magnetically inducing voltages in the secondary windings of a transformer without saturating its core. The method may be used in, but is not limited to, applications in which the transformer provides control and/or driving signals for rapid, synchronized, and/or isolated switching, of transistors or other switching devices. For example, primary control signals according to the method may be applied to one or more primary windings so as to magnetically induce the control and/or driving signals on the secondary side of the transformer.
The method includes the steps of: (a) applying to a first primary driven winding, a first set of voltages, thereby generating (i) a first current in the first primary driven winding, (ii) a first magnetic field having a first quantum of energy, and (iii) a magnetically induced second set of voltages in the first secondary winding; (b) interrupting the first current, thereby causing the first magnetic field to collapse; and (c) not later than interrupting the first current, clamping the first primary driven winding to a third set of voltages, thereby magnetically inducing a fourth set of voltages in the first secondary winding. At least one of the fourth set of voltages is less than at least one of the second set of voltages. In some aspects, step (c) includes clamping the first primary driven winding to the third set of voltages such that at least one of the fourth set of voltages is less than at least one of the second set of voltages by at least a predetermined amount.
The method may also include the step of (d) applying to a second primary driven winding a fifth set of voltages having polarities opposite to polarities of the first set of voltages, thereby generating (i) a third current in the second primary driven winding, (ii) a third magnetic field having a third quantum of energy, and (iii) a magnetically induced sixth set of voltages in the first secondary winding having polarities opposite to polarities of the second set of voltages. In some implementations, the first and second primary driven windings may be the same winding. In some aspects, further steps include (e) interrupting the third current, thereby causing the third magnetic field to collapse, and (f) not later than interrupting the third current, clamping the second primary driven winding to a seventh set of voltages, thereby magnetically inducing an eighth set of voltages in the first secondary winding. A magnitude of at least one of the eighth set of voltages is less than a magnitude of at least one of the sixth set of voltages. The term xe2x80x9cmagnitudexe2x80x9d is used in this context to avoid confusion due to the use of negative values as compared to the voltage values of the first through fourth sets of voltages. In particular, the sixth and eighth sets of voltages may have negative values as compared with the second and fourth sets of voltages, which may illustratively be assumed to have positive values. For example, a voltage value in the sixth set may be xe2x88x9218 volts and a voltage value in the eighth set may be xe2x88x926 volts. The magnitude of the value of xe2x88x926 volts should be understood to be less than the magnitude of xe2x88x9218 volts, as used herein, even though xe2x88x9218 is a smaller number than xe2x88x926 in the sense that it is more negative. The sixth and eighth sets of voltages are included in the first control and driving signal.
Step (f) may further include clamping the second primary driven winding to the seventh set of voltages such that a magnitude of at least one of the eighth set of voltages is less than a magnitude of at least one of the sixth set of voltages by at least a predetermined amount. The first set of voltages may include a voltage pulse having a substantially constant amplitude. The fifth set of voltages may include a voltage pulse having a substantially constant amplitude and having opposite polarity to the voltage pulse of the first set of voltages.
In some aspects of the method, the one or more primary windings include a primary clamp winding. In these aspects, step (a) may further include (i) applying the first set of voltages to the first primary driven winding from a voltage supply having an output and a return, thereby generating the first current in a first current path including from the output to the return, (ii) providing, not later than interrupting the first current, a second current path for a second current from the return to the output through at least the primary clamp winding wherein the second current generates a second magnetic field having substantially the first quantum of energy, and (iii) maintaining the second current path for a period of time such that the first quantum of energy is returned to the power supply. In yet further aspects, the method includes (d) applying to a second primary driven winding of the one or more primary windings a fifth set of voltages having polarities opposite to polarities of the first set of voltages. In these further aspects the primary clamp winding may include the second primary driven winding.
The primary clamp winding in some aspects of the method may have a first number of turns, the first primary driven winding may have a second number of turns, and the secondary winding may have a third number of turns. In these aspects, a first ratio between the first number and second number, and a second ratio between the first number and the third number, are determined so that a first voltage magnetically coupled to the secondary winding by the first primary driven winding when the first magnetic field is generated is greater than a second voltage magnetically coupled to the secondary winding by the primary clamp winding when the second magnetic field is generated. The first voltage in some implementations is greater than the second voltage by at least a predetermined amount.
In yet other aspects of the present invention, an apparatus is described that a transformer having a core, one or more primary windings, and one or more secondary windings. The apparatus also has a controller that provides primary control signals for magnetically induce voltages in the secondary windings without saturating the core. The controller (a) applies to a first primary driven winding a first set of voltages, thereby generating (i) a first current in the first primary driven winding, (ii) a first magnetic field having a first quantum of energy, and (iii) a magnetically induced second set of voltages in the first secondary winding, (b) interrupts the first current, thereby causing the first magnetic field to collapse, and (c) not later than interrupting the first current, clamps the first primary driven winding to a third set of voltages, thereby magnetically inducing a fourth set of voltages in the first secondary winding, wherein at least one of the fourth set of voltages is less than at least one of the second set of voltages.
The above aspects and implementations of the present invention are not necessarily inclusive or exclusive of each other and may be combined in any manner that is nonconflicting and otherwise possible, whether they be presented in association with a same, or a different, aspect or implementation of the invention. The description of one aspect is not intended to be limiting with respect to other aspects. In addition, any one or more function, step, operation, or technique described elsewhere in this specification may, in alternative aspects, be combined with any one or more function, step, operation, or technique described in the summary. Thus, the above aspects are illustrative rather than limiting.